1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having at least one rib with a discrete projection thereon that reduces the tendency of the rib to develop cracks in operation. The invention is further directed to a grinding wheel to form one or more ribs, according to the invention, on a power transmission belt.
2. Background Art
V-ribbed belts are used in a wide range of environments. V-ribbed belts are preferred for their high power transmission capability which is attributable to the increase in contact area between the ribs on the belt and cooperating pulleys.
In operation, there is a tendency of the ribs on this type of belt to crack. These cracks typically originate at the free ends of the ribs, remote from the roots thereof, or at the transition between the inwardly (or outwardly in the event of a double-ribbed belt) facing rib surface portions and the pulley-engaging side surface portions. These cracks tend to grow as the belt operates and may progress to the point that the ribs chip. The cracks may ultimately extend fully to the load-carrying cords, which may sever. The result is that the performance of the belt may be comprised. Premature failure may also result.
This cracking problem is particularly prevalent in serpentine drive systems in which a flat, outside surface of the V-ribbed belt is forcibly engaged by a flat pulley. These systems, typically used on automobile engines, have idler pulleys with flat surfaces to be pressed against the back surface of the belt to maintain a desired tension thereon.
One attempted solution to this cracking problem is described in Japanese Patent Publication No. 59-4196. FIG. 5 herein shows a belt incorporating the invention in Japanese Patent Publication No. 59-4196. The V-ribbed belt at 10 in FIG. 6 has a plurality of ribs 12, each having a free end with an inwardly facing surface portion 14. A thin layer 16 of elastic rubber is applied to the surface portion 14. The belt 10 has a plurality of laterally extending, short fibers 18 embedded in the ribs 12 for reinforcement thereof.
The ribs 12 are typically formed using a cutting or grinding wheel having surfaces that are roughened by abrasion or by adhering thereto diamond particles through an electrodeposition process. The roughened cutting/grinding surfaces tend to tear the embedded, short fibers 18 out of the ribs 12 at the surface portion 14 and/or at convex transition surface portions 20 between the surface portion 14 and the pulley-engaging side surface portions 22,24.
While the tearing out of the fibers creates only a slight scratch on the exposed belt surface, the scratches tend to grow, particularly when the belt 10 is run under severe conditions, such as at high temperatures or when it is wrapped around a small diameter pulley and is required to severely flex.
Another problem with the prior art belt in FIG. 5 is that the entire exposed surface of the ribs 12 is cut/ground during manufacture. The rib rubber is removed in chips which must be cleaned away from the working area and disposed of as industrial waste.